Stimuli-responsive gels which change in structure in response to an external change in environment, such as pH or temperature, are attracting attention as next-generation soft materials which on its own provides a sensor function, a processor function, and an effector function. Attempt has been made especially in the environment and medical fields to synthesize a stimuli-responsive gel which swells or shrinks upon recognizing specific molecules (molecule recognition capability).
For example, the inventors of the present invention have so far suggested stimuli-responsive gels which respond to disease-causing signaling biomolecules and endocrine disrupting chemicals. In these molecule-responsive gels, the reversible crosslinking sites of the gel formed by bonding with target molecules are exploited. See, for example, non-patent literatures 1 and 2.
Particles, especially, nanosize particles, have been vigorously investigated as new materials for sensor, separation, and adsorption, for example. The stimuli-responsive gel particle which changes in structure in response to an external change in environment is particularly promising, owing to the large surface area in comparison to the volume, for future applications in environmental conservation, for example, as a material which adsorbs/removes environmental contaminates, and in medicine, for example, as a device for use in drug delivery systems. Many species of pH-responsive gel particles and temperature-responsive gel particles of that nature have been reported. See, for example, patent literature 1 and non-patent literatures 3 and 4.
Non-patent literature 3 mentioned above reports a method for synthesizing pH-responsive gel particles by emulsion polymerization involving no use of emulsifier from 2-(N,N-diethylamino) ethyl methacrylate (DEAEMA) as a primary monomer in the presence of a dispersion stabilizer and a crosslinking agent.
Meanwhile, non-patent literature 4 is an up-to-date summary introducing various past and current researches on stimuli-responsive gel particles which change in size in response to pH, temperature, and other stimuli.
Patent literature 1 discloses a hollow particle which changes in transmittance in response to changes in at least one environment condition, such as pH, temperature, or light.